Method and device for controlling gas cutting operation

ABSTRACT

A method and device for controlling a gas cutting operation comprising a photosensitive element provided at a location on the gas cutting device in alignment with the path of cutting oxygen and its ejection vent to accept light emanating from the oxidation reaction portion of the cutting flame. The photosensitive element produces an electric output voltage when the luminous output from the oxidization reaction at the gas cutting impinges onto the element. The output voltage varies according to the variation of the intensity of the luminous output. The gas cutting device is controlled in response to the electric output voltage of the photosensitive element to stop running or to stop the supply of gases according to a predetermined program.

Waite States atent 91 iiayasaki et a1.

[ METHOD AND DEVICE FOR CONTROLLING GAS CUTTING OPERATION [75] inventors: I-Iidehiko Hayasaki; Eiji Kawakami,

both of Tokyo, Japan [73] Assignee: Kabushiki Kaisha Tanaka Seisakusho, Tokyo, Japan 22 Filed: Jan. 21, 1972 21 Appl. No.: 219,629

[30] Foreign Application Priority Data Aug. 28, 1973 Primary Examiner-W. W. Stallard Attorney-Richard C. Sughrue, Robert V. Sloan et a1.

[57] ABSTRACT A method and device for controlling a gas cutting operation comprising a photosensitive element provided at a location on the gas cutting device in alignment with the path of cutting oxygen and its ejection vent to accept light emanating from the oxidation reaction portion of the cutting flame. The photosensitive element produces an electric output voltage when the luminous output from the oxidization reaction at the gas cutting impinges onto the element. The output voltage varies according to the variation of the intensity of the luminous output. The gas cutting device is controlled in response to the electric output voltage of the photosensitive element to stop running or to stop the supply of gases according to a predetermined program.

11 Claims, 10 Drawing Figures Patented Aug. 28, 1973 4 Sheets-Sheet 1 lid Patented Aug. 28, 1973 w 5 4 Shuts-Shoot 4.

METHOD AND DEVICE FOR CONTROLLING GAS CUTTING OPERATION BACKGROUND or THE INVENTION 1. Field of the Invention The present invention relates to a method and device for controlling a gas cutting operation, more particularly to a method and device for controlling a gas cutting operation by detecting a variation in luminosity at the oxidation reaction portion of the cutting flame.

2. Description of the Prior Art:

In conventional automatic gas cutting devices, such as a frame planer type or a type used in a numerical controlling system having the main frame of the cutting device moved over two parallel rails, there is no interlinkage between the cutting flame ejected from a nozzle mounted on a blow pipe attached to the frame of the cutting device and the work piece to be cut, such as a steel plate. Accordingly, other than observation by the operator there has been no definite means to detect a misflring of the cutting flame which results in an interruption of the gas cutting operation. For instance, in the frame planer type a plurality of cutting nozzles are provided on a frame and the frame ismoved over the rails for cutting a plurality of parallel lines at once. If one of the plurality of the nozzles has misflring the cutting operation is interrupted only for the particular cutting nozzle while all the other nozzles are operating properly. But in this case the cutting operation should be carried by moving the frame again. In order to avoid such misoperation a manual supervision is indispensable which makes the operation coat high.

Also in the numerical control system, should a misflring occurs in the cutting nozzle, the movement of the nozzle driven by the numerical controlling equipment is continued for sometime before the device is stopped under control of the operator. In such a case the numerical controlling devices had made already some steps after the disabling of the nozzle. This time an accurate controlling operation is disturbed; Almost the same problem arises in an optical tracing type gas cutting device.

Accordingly for the above kinds of the conventional automatic gas cutting devices the manual supervision is inevitable which possibly causes some mulfunctioning.

SUMMARY OF THE INVENTION One object of the present invention is to mitigate the aforementioned disadvantages of conventional gas cutting systems.

A further object of the present invention is to provide a method and device for automatically controlling a gas cutting operation by automatically controlling the cutting velocity to a desired value and by automatically stopping the device at a desired time, such as at a misfiring.

The present invention comprises a novel method and device for controlling a gas cutting operation in which an illumination detecting and/or measuring means is provided at a position in alignment with the oxidization reaction portion of the cutting flame and through the path of the cutting oxygen which automatically supervises the conditions of the gas cutting, such as the cutting velocity, completion of the cutting operation, misflring of the cutting flame, etc. by means of detecting variation in the luminance at the oxidation reaction portion of the cutting flame.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a front view of automatic gas cutting device to which the present invention can be applied;

FIG. 2 shows a cross-section of the blow pipe and nozzle portion of a gas cutting device in accordance with the present invention;

FIG. 3 is an embodiment of the cutting nozzle of FIG. 2 viewed from the direction shown by arrows AA in FIG. 2;

FIGS. 4(A) (C) are schematic representations of view presented to a photosensitive element used in accordance with the present invention;

FIG. 4(D) is a schematical representation of the progress of the cutting operation at a cross section of the work piece;

FIG. 5 is .a graph showing a typical relationship between the detected output voltage from the photosensitive element and the cutting velocity of the cutting de vice;

FIG. 6 is an example of an oscillogram showing the actual output voltage of the photosensitive element of the present invention during a cutting operation; and

FIG. 7 is a block diagram showing one example of controlling circuit of the gas cutting device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depicts the working principles and basic construction of an example of an automatic gas cutting device to which the present invention can be applied. In FIG. 1, the frame 2 of a gas cutting device is mounted to move along rails l, l' by means of wheels 3, 3'. The frame 2 is controlled to run over the parallel rails l, 1'

by driving means 4 provided at the main end portion of the frame 2, which is in turn controlled by operating panel 5. A moving table 6 movably mounted on the main body of the frame 2 in the longitudinal direction comprises a blow pipe 7 having its cutting nozzle mounted over a work piece 8 carried on working frame 9. In FIG. 1, two moving tables 6, 6' are shown. The details of driving means 4 and controlling panel 5 are set out as such portions are not an essential part of the present invention.

The usual practice in gas cutting is to first heat the immediate portion of the work piece to be cut, such as a steel plate, by means of a preheating flame consisting of a mixture of fuel gas and oxygen. When the portion of the steel plate to be cut is sufficiently heated, high pressure cutting oxygen is then ejected onto the work piece to cause a strong oxidizing reaction between the work piece and the cutting oxygen stream. By this oxidizing reaction, the work piece, such as a steel plate, is heated to melt and the resultant molten slag is blown off the cutting portion by the kinetic energy of the oxygen stream, whereafter the cutting operation may be continued by relative movement between the nozzle and the work piece.

The present invention was reached based on the idea that the luminance at the oxidizing portion of the flame varies according to the condition or state of the gas cutting operation, more particularly to the conditions, such as initiating, the cutting, the cutting velocity and misfiring or completion of the cutting operation. In accordance with the present invention, the variation in the luminance during different conditions of the cutting operation is detected by a photoelectric detecting means provided in alignment with said luminance producing portion of the work piece, i.e., the part of the work piece to be cut.

FIG. 2 depicts a cross-section of one example of a blow pipe and cutting nozzle portion of a gas cutting device in accordance with the present invention. As shown in FIG. 2, a blow pipe 7 carries a cutting nozzle 10 secured to its lower end by means of a securing nut 11. The cutting nozzle 10 is provided with a central path 12 for the cutting oxygen and a plurality of holes 13 surrounding said central path 12, for ejecting a preheating flame. FIG. 3 shows end view of the cutting nozzle 10, in which the arrangement of the holes is shown more clearly. The preheating flame consists of mixture of preheating oxygen introduced into the holes or paths 13 via mixer portions 14 through a path 18 in blow pipe 7 supplied from a supply hose 19 and fuel gas supplied from a supply hose 21 through path 20in blow pipe 7 into the mixer portion 14 of the cutting nozzle 10. The above configuration of the device is just same as that of the conventional device and hence further detailed explanation is omitted. It is to be noted that the blow pipe 7 is mounted onto the above mentioned moving table 6 shown in FIG. 1 to move over the work piece 8 and the height between the work piece 8 and the relative position such as the running direction or the velocity are controlled by the driving means 4. In FIG. 2, 26 shows schematically a cutting groove formed by the cutting oxygen.

The blow pipe 7 has a central hole through which passes the cutting oxygen supplied from a hose 17 through branch hole 16 provided in blow pipe 7. According to the present invention, the central hole 15 is extended'vertically up to the top of the blow pipe 7. At the top of the blow pipe 7 an outer threaded pipe 30 is secured, and a photosensitive element 22, such as a photodiode, is provided by means of a securing nut 23, preferably also enclosing-protecting transparent glass 24. The photosensitive element 22 is arranged in visual alignment with said center hole 15 of the blow pipe 7 which in turn is aligned with the central path 12 of the nozzle 10 for the cutting oxygen. Leads 22, 22' are connected to the photosensitive element 22, to derive the electric output voltage of the element in a manner known to the art. The connecting leads 22' are connected to the input of a controlling device, which will be explained later on, for the gas cutting device. By this arrangement the buring or oxidizing reaction portion of the work piece is in visual contact with the photosensitive element 22 and accordingly, the element produces an output corresponding to the intensity of illumination.

Referring now to FIG. 4, the relationship between the cutting speed of the cutting device and the intensity of illumination impinging upon the photosensitive element will be explained. In each figure of FIGS. 4(A), 4(8) and 4(C), circle 25 represents the general view presented to the photosensitive element 22 provided at the top of blow pipe 7 via the path 15 and cutting oxygen hole 12 of nozzle 10 as shown in FIG. 2. Referring to FIG. 4, 26 depicts the cutting groove in the work piece 8 where the molten slag is blown off, and 26' is side edge of the cutting groove 26.

FIG. 4(A) shows the condition where the cutting velocity is kept at a suitable value.

Such a suitable valve of the cutting velocity varies depend on the cutting nozzle, cutting requirement and the thickness of work pieces. However, it is to be noted that for an ordinary type cutting nozzle used for cutting a steel plate having the thickness between 12.7 mm to 25.4 mm (A 1 inch) the suitable cutting velocity for high quality cutting is about 400 to 600 millimeter per minute-Under such condition, the molten slag is blown off by the high speed ejection stream of the cutting oxygen and the progressing front face of the cutting operation is extended substantially normal to the surface of the work piece. In this case, the luminous output which impinges onto the photosensitive element 22 from the oxidization reaction portion emanates from the hatched portion 27 where a very strong oxidizing reaction exists.

FIG. 4(B) shows the condition in which the cutting velocity is made slightly higher. In this case, the front face of the cutting blow is bent to form a drag having length d as shown in FIG. 4(D) and the area of luminance producting portion of the work piece becomes somewhat larger, as shown by 27' in FIG. 4(B).

FIG. 4(C) shows the case of the occurrence of a misfiring. The cutting nozzle has moved out of the cutting groove 26 to face on the steel plate and the cutting operation is interrupted. In this case, no light impinges ontophotosensitive element 22 due to the lack of high temperature oxidation.

As explained above, the quality of light impinging onto the photosensitive element varies according to the variation of the cutting velocity. Namely, the quantity of light increases according to the rise of the cutting speed and at the time of misfiring no brightness is observed. Speaking very strictly, the intensity of light at the oxidization portion varies according to the variation of the cutting speed. But it had been turned out that such variation can be disregarded in practice after a number of experiments.

As mentioned above, the present invention is based on the concept of detecting the variation of illumination at the oxidizing reaction portion of a work piece undergoing a gas cutting operation by photosensitive element which produces a variation in output voltage dependent upon the illumination impinging thereon, the variation in output voltage of the photosensitive element being amplified and used to control the gas cutting device. g

In one particular embodiment of the invention, the interval between the top of nozzle 10 and the steel plate 8 is 10 mm, and the distance between the top of the nozzle 10 and the photosensitive element 22 is mm. As for the photosensitive element 22, a photodiode of the photoelectronic type is used and leads 22 are connected to an oscilloscope to provide a measurement of the variation of the voltage and the luminance. The result of this measurement will be explained hereinafter.

The measured output voltage on the oscilloscope will be zero at the start of preparation of the gas cutting operation, namely, the firing, the adjustment of the preheating flame, until the actual beginning of the preheating at the beginning edge of the steel plate. This voltage will slightly rise up when the end surface is reached to a firing temperature of about 950 C and shows a considerable increase at the time of ejection of the cutting oxygen at start of the cutting operation which causes a very strong oxidizing reaction at a melting temperature of about l,600 C or more.

FIG. 5 is a graph showing a typical relationship between the cutting velocity and the detected voltage observed on an oscilloscope, wherein the diameter of the cutting oxygen was 1.3 mm and the thickness of the steel plate was 25 mm. No practical difference was observed when the interval between the tip of the nozzle and the steel plate was in-the range of 10 mm and 80 mm. This fact proves that the detecting method of the present invention offers a high accuracy of detection for a considerable range of the height of nozzle over the work piece. When the cutting operation is interrupted by misfiring to cause the nozzle to face unmelted steel plate or when the cutting operation is terminated and no oxidizing reaction is effected, the detected voltage suddenly decreases to mV.

In the case of non vertical cutting operation, the apparent plate thickness for cutting is slightly increased by the oblique cutting direction, and then a slightly higher detecting voltage is observed. Also, at the time of a boring operation generally known in the art as piercing operation the detected voltage shows a clear and apparent increase at the time of the start of the oxidizing reaction when the preheating operation is changed to the boring. However, the method of the present invention may equally applied to such cases in practice without particular difficulty.

FIG. 6 is a sketch of actual oscillogram observed in operation of a device made in accordance with the present invention. This oscillogram is taken for cutting a steel plate of 25 mm thick and at a nozzle height of 10 mm. The ordinate of this oscillogram is the detected voltage derived from the photosensitive element 22.

' One scale corresponds 100 mV approximately. The abscissa of the graph is the time interval for changing the cutting velocity as indicated by the number. One unit scale corresponds about seconds. The point 1 is the beginning of the preheating operation. As seen by the oscillogram the portion between point 1 to point 2 corresponds to the preheating condition. Point 2, where a peak of output voltage occurs, corresponds to the start of cutting by injecting cutting oxygen onto the preheated portion of the work piece. The actual output voltage shows substantial fluctuation but it can be made averaged by using a suitable electric circuit. The numerals 200, 400, 600, 800, 800 indicate that the nozzle is relatively moved in a speed of 200 mm/min., 400 mm/min. 800 mm/min. and over 800 mm/min. The point 3 indicates a flame out due to a too high relative speed of the nozzle 10. As shown by the graph the curve suddenly decreases to 0 mV at the flame out.

FIG. 7 is a block diagram showing schematically an embodiment of the controlling system using the detected output voltage of the present invention. In FIG. 7, blow pipe 7 and nozzle 10 are the main portion of the gas cutting device as explained above with reference to FIG. 2. The detected output voltage from the photosensitive element 22 is supplied to an amplifier 32 via out put leads 22'. In this amplifier 32 the output voltage is amplified and then supplied to an integrating circuit 34 which effects a wave shaping to smooth out the minor fluctuation of the output voltage. A misfire control circuit 40 is connected to the wave shaping circuit 34. Should a misfiring occurs causing the output voltage suddenly decreases to 0 volt, the misfire control circuit 40 operates to control magnetic valves 61, 63, 65 via controlling circuits 60, 62, 64. The valves are inserted in the supply paths of cutting oxygen, preheating oxygen and fuel gas supplied to the cutting device via hoses 17, 19, 21, respectively and supplied from a main oxygen storage 50 through regulators 54 and 56 and from a main fuel storage 52 through a regulator 58. The misfire control circuit also sends out an instruction signal to a drive control circuit 44 and stops the driving of the main driving motors 46 and 48. Said misfire control circuit also operates an alarm device 42 to call the attention of the attendant. In normal condition the output voltage from the wave shape circuit 34 is supplied to a comparator 36, in which the voltage is compared with reference voltages V and V Said reference voltages may preferably be chosen to the corresponding values with the upper and lower limits for the suitable cutting speed, for instances 400 600 mm/min. If the output voltage exceeds the maximum limit or decreases under the minimum level set by the reference voltages V and V an output voltage is supplied to a control unit 38 which in turn actuates the drive control circuit 44 to maintain the driving speed of the driving motors 46 and 48 to be within the aforementioned suitable range.

It should be noted that FIG. 7 is only one possible embodiment and the present invention is not limited to the particular circuit only. There are many variations in the controlling circuit.

As is clearly explained above, according to the present invention the detected voltage shows a remarkable variation at the time of an interruption of the cutting operation due to possible misfiring or at the time of termination of the cutting operation of the device when the oxidizing reaction is terminated, and it also shows a considerable variation at a variation in the cutting velocity during the cutting operation. Accordingly, by using the output voltage deviation obtained from the photosensitive element and after amplification, and suitable processing the desired automatic controlling operations of the gas cutting device, such as stopping of the oxygen and the fuel gas, stopping of the gas cutting device and velocity-control of the same, can be effected. Therefore, the present invention affords great advantages in improving the efficiency of a gas cutting device.

What is claimed is:

l. A method for controlling the velocity of a gas cut ting operation comprising the steps of detecting a variation in the luminance of an oxidizing reaction at the point of impingement of the gas cutting flame on a workpiece by means of a photosensitive element disposed in optical alignment with said point, said element producing a variable output voltage in response to a variation in said luminance and using the obtained output voltage representing said luminance variation for controlling the velocity of a gas cutting operation.

2. The method for controlling the velocity of a gas cutting operation as claimed in claim 1, wherein the gas cutting operation is stopped when a misfiring is de- 5. A gas cutting device comprising means to detect a variation of luminance at the oxidizing reaction portion of the cutting flame of a cutting device, means to detect an electric output voltage detected by said means and means to control the velocity of the gas cutting operation of the device in response to the electric output voltage.

6. The gas cutting device as claimed in claim wherein the luminance detecting means is a photosensitive element.

7. The gas cutting device as claimed in claim 6, wherein the photosensitive means is a phototransistor.

8. The gas cutting device as claimed in claim 5, wherein the photosensitive element is mounted in optical alignment with the luminant portion via the path way for the introduction of cutting oxygen in said cutting device.

9. The gas cutting device as claimed in claim 5, wherein the photosensitive element is mounted at the top of a blow pipe and aligned with the luminance portion of the flame through a central path for the cutting oxygen in the blow pipe and through a hole provided in the nozzle of the blow pipe.

10. A gas cutting device comprising a blow pipe and a nozzle provided with path ways for cutting oxygen,

preheating oxygen and fuel gas, a photosensitive element disposed on the blow pipe in alignment with the cutting flame through the cutting oxygen path way to produce an electric output voltage in proportion to the cutting speed of the gas cutting device.

11. An automatic gas cutting device controlling system comprising a blow pipe and a nozzle provided with path ways for cutting oxygen, preheating oxygen and fuel gas, a photosensitive element is equiped on the blow pipe in alignment with cutting flame through the cutting oxygen path way to produce an electric output voltage in proportion to the cutting speed of the gas cutting device and further comprising an amplifier, a wave shaping circuit, a comparator, a control unit, a misfire control circuit and a drive control circuit, wherein the misfire control circuit detects zero voltage condition of the output voltage derived from the photo sensitive element and stops the running of the device and stops the supply of fuel gas and oxygen, and the comparator compares the derived output voltage with predetermined reference voltages to control the running of the gas cutting device within a predetermined moving speed. 

2. The method for controlling the velocity of a gas cutting operation as claimed in claim 1, wherein the gas cutting operation is stopped when a misfiring is detected by an output voltage of zero voltage.
 3. The method for controlling the velocity of a gas cutting operation as claimed in claim 1, wherein the supply of cutting oxygen, preheating oxygen and the fuel gas is stopped automatically when a misfiring is detected by an output voltage of zero voltage.
 4. The method for controlling the velocity of a gas cutting operation as claimed in claim 1, wherein the cutting velocity is controlled to be within a predetermined range by detecting the variation of the output voltage.
 5. A gas cutting device comprising means to detect a variation of luminance at the oxidizing reaction portion of the cutting flame of a cutting device, means to detect an electric output voltage detected by said means and means to control the velocity of the gas cutting operation of the device in response to the electric output voltage.
 6. The gas cutting device as claimed in claim 5 wherein the luminance detecting means is a photosensitive element.
 7. The gas cutting device as claimed in claim 6, wherein the photosensitive means is a phototransistor.
 8. The gas cutting device as claimed in claim 5, wherein the photosensitive element is mounted in optical alignment with the luminant portion via the path way for the introduction of cutting oxygen in said cutting device.
 9. The gas cutting device as claimed in claim 5, wherein the photosensitive element is mounted at the top of a blow pipe and aligned with the luminance portion of the flame through a central path for the cutting oxygen in the blow pipe and through a hole provided in the nozzle of the blow pipe.
 10. A gas cutting device comprising a blow pipe and a nozzle provided with path ways for cutting oxygen, preheating oxygen and fuel gas, a photosensitive element disposed on the blow pipe in alignment with the cutting flame through the cutting oxygen path way to produce an electric output voltage in proportion to the cutting speed of the gas cutting device.
 11. An automatic gas cutting device controlling system comprising a blow pipe and a nozzle provided with path ways for cutting oxygen, preheating oxygen and fuel gas, a photosensitive element is equiped on the blow pipe in alignment with cutting flame through the cutting oxygen path way to produce an electric output voltage in proportion to the cutting speed of the gas cutting device and further comprising an amplifier, a wave shaping circuit, a comparator, a control unit, a misfire control circuit and a drive control circuit, wherein the misfire control circuit detects zero voltage condition of the output voltage derived from the photosensitive element and stops the running of the device and stops the supply of fuel gas and oxygen, and the comparator compares the derived output voltage with predetermined reference voltages to control the running of the gas cutting device within a predetermined moving speed. 